Tic-TACs: refreshing hair growth

Abstract

Although stem cells are subject to niche control, evidence is emerging that they also contribute to generating the niche through their offspring. Using the hair follicle as a model, Hsu at al. demonstrate that the transient-amplifying cells, downstream of stem cells and well-known cell producers, signal back to stem cells to maintain long-term regenerative capacity.

Figure 1. TACs Regulate HF SC Proliferation

(A) During HF regeneration, signals from the DP evoke proliferative responses in activated stem cells (A-SCs) located in the HG below a layer of quiescent Bu-SCs, leading to the initiation of the growth of the HF. (B) HG proliferation leads to the production of TACs and expansion of the HF area downward, leading to increased distances (Δd) between the DP and the SC populations. After initiation of HF growth, BU-SCs begin to proliferate by unknown mechanisms. (C) Hsu et al. now show that SHH signals emanating from TACs directly stimulate BU-SC proliferation as well as the DP to secrete Noggin (Nog) and Fgf7, which feed back to TACs, allowing for proper HF regeneration.